I run wfp off 110 amp leisure battery. and I use a 'ring smart charge 8' intelligent charger. cost bout 50 quid if I remember right, charges at 2/4/6/8 amp per hour. I charge it on lowest getting, takes day and half normally to charge.
Id rather spend abit more and get something that will not fry the battery, these condition batteries and can help with badly discharged or neglected batteries (apparently!). for my tuppence worth! use similar charger with motorbike,(has trickle maintain charge facility).
cheers!
Andy